Foundational Knowledge

Question 1

Earthquake Cycle

Answer 1

An earthquake is caused by a sudden release of strain in the earth’s interior (meaning the crust or mantle). The sudden release of strain occurs because the strength of the straining material is exceeded by the strain that has accumulated within that material. For example, along a fault that is locked by friction, fault rupture occurs when the accumulated strain exceeds the frictional forces that prevent fault slip.

II. The seismic “cycle”

Although not all earthquakes are caused by sudden slip along a fault, most of them are. The general concept you must keep in mind is that faults are relatively planar (flat) fractures in the crust along which rocks on either side of the fault move in different directions. Because fault surfaces are “rough”, rocks that meet along a fault do not slide freely past each other, but are instead locked for long periods by friction along the fault. Over decades to millenia, strain builds up within the rocks that are separated by the fault as their movement is prevented by along-fault friction. At some point, the amount of strain exceeds the frictional forces that are preventing slip. The fault ruptures and rocks on either side of the fault slide rapidly as the pent-up strain is relieved. The moment of rupture is when the earthquake occurs. For obvious reasons, the earthquake cycle is frequently referred to as a “stick-slip” process - long periods of “stick” are followed by a short period of “slip”, and the process then repeats itself.

The seismic “cycle” refers to the observation that earthquakes repeatedly rupture a given part of a fault. The term “cycle” does not however imply that earthquakes are a periodic or regularly repeating event (in other words, “cycle” does not imply that earthquakes are a natural phenomenon that have clocklike behavior like the rising and setting of the sun).

The seismic cycle can be divided into three periods, consisting of inter-seismic slip, co-seismic slip, and post-seismic slip. Two of these three phases are illustrated by the following figure, namely, the period of slow accumulation of elastic strain that coincides with frictional locking of a fault between earthquakes (the interseismic phase), and the sudden rupture that is the earthquake (the coseismic phase). The term “elastic” refers to a particular type of rock deformation, namely deformation that can be “recovered” at a future point. Elastic materials have “memory” of their original shape. If their shape is changed because a force is imposed on them, they will return to their original shape if the force is removed. A rubber band is an excellent example of an elastic material. So are rocks, provided that their temperatures aren’t too high.

Question 2

Mag-Frequency Plots

Answer 2

Easier to isolate the Fundemental waves that comprise a signal

Question 3

History of Plate Tectonics

Answer 3

• fundamental theory of geosciences
• explains diverse E phenomena
• continent reshapes E’s surface
• affected how life on Earth evolved

Question 4

Cross-section of plate boundaries

Answer 4

lithosphere - cold, brittle outer shell of Earth that includes crust + upper part of mantle to ~100 km depth beneath lithosphere is asthenospherehotter, softer layer where rocks can flow (located entirely in mantle) over which tectonic plates move.

Question 5

Layers of Earth

Answer 5

Lithosphere (crust and upper-most solid mantle)
Asthenosphere
Mantle
Outer Core (liquid)
Inner Core (solid)

Question 6

Volcano type and silica content, eruption style, viscosity

Answer 6

cinder, composite, shield, lava domes. silica content is the amount in magma. eruption style = effusive and quiet or explosive and loud. viscosity = the resistance of a fluid flow, resulting from cohesion of its particles

Question 7

Stream hydrographs and impact of urbanization on floods and hydrographs

Answer 7

Show variation in flow during a normal year

Normal -> event -> receding

Question 8

Flood frequency curves

Answer 8

the probability that a flood of a given size will occur during a given time

Question 9

Impacts of floods

Answer 9

positives: recharges groundwater
adds nutrients
negatives: requires fighting
damage property and infrastructure
loss of life

Question 10

Sediment transport/deposition/erosion

Answer 10

• Stream,s especially those in Mt. areas, are carved into bedrock
• “Bedrock Streams”
• If bedrock hard, shape defined by geology, if bedrock soft, stream has reign to carve out own shape

Question 11

Meandering Streams

Answer 11

deposition occurs at a point bar
momentum of river follows the thawleg
sinuous, looping curves (meanders)
cut bank erodes; point bar grows

Question 12

Changing base level

Answer 12

Tectonic uplift can significantly change base level
  ... and so can changing sea level
Incised canyons due to renewed
uplift + downcutting
Downcutting can result in rivers
flowing through rugged topography